This invention relates to a method of downhole fluid separation and displacement, and a plug utilized in the method.
In connection with the formation and use of downhole pipes, or pipelines, for conducting fluids, such as hydrocarbons, and the like, from one location to another, it is often necessary to pass different fluids through the pipe to perform different operations. In these techniques, the fluids often have to be isolated from each other in the pipe to prevent them from mixing in the pipe and to prevent one fluid from contaminating the other.
Therefore, a separating, or displacement, plug has evolved which is introduced into the pipe above one of the fluids after which the other fluid is introduced into the pipe above the plug and thus displaces the plug and the first fluid from the pipeline. Once these operations are completed, the plug is usually drilled out for removal from the pipe. However, it is difficult to remove the pieces of the plug from the pipe after the plug has been drilled out, especially in connection with offshore drilling operations in which the pieces must pass to the top of the well bore and then to the offshore rig through a relatively long riser connecting the rig to the well bore and containing sea water and drilling fluid. Therefore, in these situations, various chemicals usually have to be introduced into the riser and/or the well bore to change the viscosity of the fluids to permit recovery of the plug pieces, which is time-consuming and costly.
Therefore, what is needed is a plug that, when drilled out in accordance with the foregoing, can be easily and quickly removed from the pipe, and through the riser, if applicable, and to the surface after it has been drilled out.